Maybe the roots down in the mix are dead since overwatering kills those roots further down a lot faster. When I have an overwatered orchid with a few good roots left, I'd repot it in new mix. (The old mix could have broken down and "choked" the roots, or the roots simply died of being soaked all the time.) It's a good thing you can still see some white roots. Those should keep the plant going until it puts out new roots on new growths. Try to raise the humidity to keep the plant more comfortable.